Field of the Invention
The present invention is directed to the manufacture of acrylonitrile. In particular, the present invention is directed to an improved process for the manufacture of acrylonitrile utilizing a fluid bed reactor.
The process for manufacturing acrylonitrile in a fluid bed reactor has been practiced commercially since the early 1960's. Typically, the reactor effluent from the propylene ammoxidation reaction in a fluid bed reactor is passed through a quench column, absorption column and recovery stripper columns to purify and recover the acrylonitrile product. Generally, a water stream is used to absorb the product organics (acrylonitrile, acetonitrile and HCN) from the vapor stream in the absorption column. The product organics removed in the absorption column are then stripped from the water stream in the recovery stripper columns. Typically, the absorption column contains three sections: (1) a lower heat transfer zone where hot gases from the quench are cooled by direct heat exchange with cold water; (2) an absorption zone where organics in the reaction gases are absorbed into a chilled water (the resultant water, rich with organic product is called a "rich water"); and (3) an upper heat transfer zone where incoming water is cooled by direct exchange with the cold strip gas. In prior art procedures, the internals for these three sections of the absorption column typically comprise refractionation trays or structured packing or random packing. The present invention is directed to an improved process for the manufacture and recovery of acrylonitrile which results in improved run time due to elimination of polymer fouling problems in the absorption column.